Backlight device and liquid crystal display

ABSTRACT

A back-light device and a liquid crystal display in which light from light sources is guided to a light-guiding plate efficiently and heat of the light sources is dissipated efficiently. The back-light device of the liquid crystal panel has a front frame and a rear frame. There are provided four optical sheets, a light-guiding plate, a flexible PCB, two light sources, and a reflecting sheet between the front frame and the rear frame. The flexible PCB has a PCB part and two erected parts. A resistor and a thermistor as electronic parts and two light sources are installed on the PCB part in the vicinity of the erected parts. A light-radiating surface of the light source is pressed to an incident surface of the light-guiding plate by the erected part.

TECHNICAL FIELD

This invention relates to a back-light device and a liquid crystaldisplay.

BACKGROUND ART

A back-light device to radiate light to the back of a transmission-typeliquid-crystal panel is available (patent literature 1), wherein lightis radiated from the light-radiating surfaces of LED light sources,enters a light-guiding plate through its incident surface, and isdiffused in the light-guiding plate and directed to the back of theliquid-crystal panel.

The back-light device comprises (i) a printed circuit board on which theLED light sources are installed, (ii) the light-guiding plate, (iii)optical sheets which are disposed on one side of the light-guiding plateand direct the light to the back of the liquid-crystal panel, (iv) areflecting sheet which is disposed on the other side of thelight-guiding plate and reflects light toward the liquid-crystal panel,and (v) a frame which houses and holds the above components.

Patent literature 1: Japanese Unexamined Patent Publication No.2002-75038

The above back-light device has the following problems.

-   (1) A gap may be left between the light-radiating surfaces of the    LED light sources and the incident surface of the light-guiding    plate because of assembly errors and parts errors. In this case, it    is difficult to guide the light from the light-radiating surfaces to    the incident surface efficiently.-   (2) It is difficult to dissipate the heat of the LED light sources;    accordingly, it is difficult to feed an electric current of high    intensity to the light sources.-   (3) If the frame is grounded, or earthed, an insulating member has    to be provided between the frame and the printed circuit board to    insulate the electronic parts installed on the printed circuit board    from the frame. The insulating member increases the cost of the    back-light device.

Under the circumstances, it is an object of the present invention toprovide a back-light device and a liquid crystal display whosemanufacturing costs are low and wherein the light from light sources isguided to a light-guiding plate and the heat of light sources isdissipated efficiently.

It is another object of the present invention to provided a back-lightdevice and a liquid crystal display whose manufacturing costs are lowand wherein the electronic parts are efficiently insulated from theframe.

DISCLOSURE OF THE INVENTION

To achieve the above objects, the present invention provides aback-light device for shedding light on the back of a liquid-crystalpanel. The back-light device comprises a light-guiding plate, a flexibleprinted circuit board (hereafter called PCB), light sources, and aframe. The light-guiding plate is of the shape of a rectangular plate.Part of one of its four side surfaces, each facing in a directionperpendicular to the directions of its thickness, is formed as anincident surface to allow light to enter. One of its top and bottomsurfaces is a light-radiating surface. The flexible PCB is attached topart of the light-guiding plate in the vicinity of the incident surface.The light sources are installed on the flexible PCB. Each light sourcehas a light-radiating surface, which is put in close contact with theincident surface of the light-guiding plate. The frame houses and holdsthe light-guiding plate and the flexible PCB. The frame has a supportingwall on which the light-guiding plate is put, a window through which thelight-radiating surface faces the back of the liquid-crystal panel, anderected walls which are erected at the periphery of the supporting wall.The flexible PCB has a PCB part on which the light sources are installedand erected parts which are erected on the far side of the PCB part awayfrom the incident surface of the light-guiding plate. The light-guidingplate is positioned with respect to the frame in the direction definedbetween the incident surface and the side surface facing in a directionperpendicular to the directions of the thickness of the light-guidingplate and being opposite to the incident surface by its side surfaceopposite to its incident surface being in contact with an erected wallof the frame and the erected parts of the flexible PCB being in contactwith another erected wall of the frame.

Besides, the present invention provides a liquid crystal displaycomprising a liquid-crystal panel and a back-light device for sheddinglight on the back of the liquid-crystal panel. The back-light devicecomprises a light-guiding plate, a flexible PCB, light sources, and aframe. The light-guiding plate is of the shape of a rectangular plate.Part of one of its four side surfaces, each facing in a directionperpendicular to the directions of its thickness, is formed as anincident surface to allow light to enter. One of its top and bottomsurfaces is a light-radiating surface. The flexible PCB is attached topart of the light-guiding plate in the vicinity of the incident surface.The light sources are installed on the flexible PCB. Each light sourcehas a light-radiating surface, which is put in close contact with theincident surface of the light-guiding plate. The frame houses and holdsthe light-guiding plate and the flexible PCB. The frame has a supportingwall on which the light-guiding plate is put, a window through which thelight-radiating surface faces the back of the liquid-crystal panel, anderected walls which are erected at the periphery of the supporting wall.The flexible PCB has a PCB part on which the light sources are installedand erected parts which are erected on the far side of the PCB part awayfrom the incident surface of the light-guiding plate. The light-guidingplate is positioned with respect to the frame in the direction definedbetween the incident surface and the side surface facing in a directionperpendicular to the directions of the thickness of the light-guidingplate and being opposite to the incident surface by its side surfaceopposite to its incident surface being in contact with and erected wallof the frame and the erected parts of the flexible PCB being in contactwith another erected wall of the frame.

Thus, the erected parts of the flexible PCB put the light-radiatingsurfaces of the light sources into close contact with the incidentsurface of the light-guiding plate.

Besides, the heat of the light sources is conducted from the erectedparts of the flexible PCB to one of the erected walls of the frame.

Moreover, if the erected parts of the flexible PCB is positioned betweenthe electronic parts installed on the PCB part and the nearby erectedwall of the frame, the insulation between the electronic parts and theframe is secured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view to show the construction of the liquidcrystal display of the first embodiment of the present invention;

FIG. 2 is an exploded perspective view to show the construction of theliquid crystal display of the first embodiment of the present invention;

FIG. 3 is a plan view of the flexible PCB;

FIG. 4 is an illustration to show the positional relation between theflexible PCB and the light-guiding plate;

FIG. 5 is a sectional view of the flexible PCB;

FIG. 6 shows circuit diagrams of circuits formed on the flexible PCB;

FIG. 7 is a graph showing the relation between the ambient temperatureof the light sources and the current feedable to them;

FIGS. 8A, 8B, and 8C show other embodiments of the erected parts of theflexible PCB, wherein the flexible PCB of FIG. 8A has three erectedparts, the flexible PCB of FIG. 8B has an erected part extending alongthe PCB part, and electronic parts are installed on the erected parts inFIG. 8C;

FIG. 9 shows still another embodiment of the erected parts of theflexible PCB; and

FIG. 10 shows the construction of a back-light device of prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, embodiments of the present invention will be described byreferring to the drawings.

FIG. 1 is a sectional view to show the construction of the liquidcrystal display of the first embodiment of the present invention. FIG. 2is an exploded perspective view to show the construction of the liquidcrystal display of FIG. 1. FIG. 3 is a plan view of the flexible PCB(printed circuit board) of FIG. 2. FIG. 4 is an illustration to show thepositional relation between the flexible PCB and the light-guiding plateof FIG. 2. FIG. 5 is a sectional view of the flexible PCB of FIG. 2.FIG. 6 shows circuit diagrams of circuits formed on the flexible PCB ofFIG. 2.

As shown in FIG. 2, the liquid crystal display 100 comprises aliquid-crystal panel 10 and a back-light device 12.

The liquid-crystal panel 10 includes a transmission-type liquid-crystaldisplaying device in the shape of a rectangular plate. Theliquid-crystal panel 10 has a displaying surface 1002 on which imagesare displayed and a back surface 1004 which is opposite to thedisplaying surface 1002. The back-light device 12 sheds light on theback surface 1004 and the light penetrates the liquid-crystal panel 10toward the displaying surface 1002; thus, images are displayed on thedisplaying surface 1002.

The back-light device 12 has a front frame 14 and a rear frame 26. Thereare provided four optical sheets 16, a light-guiding plate 18, aflexible PCB 20, two light sources 22, and a reflecting sheet 24 betweenthe front and rear frames 14 and 26.

The light-guiding plate 18 is in the shape of a rectangular plate andhas four sides facing in directions perpendicular to the directions ofits thickness. One of them is formed as an incident surface 1802 toallow light to enter. Another side is formed as a first side 1808opposite to the incident surface 1802. The remaining two sides areformed as second and third sides 1810 and 1812 opposite to each otherbetween the incident surface 1802 and the first side 1808.

The light-guiding plate 18 has two surfaces facing in the directions ofits thickness. One of them is formed as a light-radiating surface 1804to radiate light. The other is formed as a back surface 1806.

Light enters the light-guiding plate 18 through the incident surface1802 and is diffused in the light-guiding plate 18 and radiated from thelight-radiating surface 1804. The light-guiding plate 18 is made ofacrylic resin.

The front and rear frames 14 and 26 house and hold the light-guidingplate 18 and the flexible PCB 20.

The front frame 14 has (i) a supporting wall 1404 which is rectangularas seen from above and supports the light-guiding plate 18 and theflexible PCB 20, (ii) a rectangular window 1402 which is formedapproximately in the center of the supporting wall 1404 and allows thelight-radiating surface 1804 of the light-guiding plate 18 to face theoptical sheets 16, and (iii) first to fourth erected walls 1406, 1408,1410, and 1412 which are erected on the four sides of the supportingwall 1404. The first and second erected walls 1406 and 1408 face eachother. The third and fourth erected walls 1410 and 1412 face each other.The front frame 14 is made of a metal.

The distance between the incident surface 1802 and the first side 1808is shorter than the distance between the first and second erected walls1406 and 1408. The distance between the second side 1810 and the thirdside 1812 is determined so that they come into contact with the thirdand fourth erected walls 1410 and 1412.

As shown in FIG. 1, the flexible PCB 20 is disposed on thelight-radiating surface 1804, in the vicinity of the incident surface1802. The flexible PCB 20 is pasted onto the light-guiding plate 18through the medium of both-sides adhesive tape 21.

As shown in FIGS. 1 to 4, the flexible PCB 20 has a belt-shaped PCB part2002 and two erected parts 2003. The PCB part 2002 is disposed at theportion of the supporting wall 1404 facing the incident surface 1802 andextends straightly along the incident surface 1802. The erected parts2003 are erected on the far side of the PCB part 2002 away from theincident surface 1802 at an interval in a direction of the extension ofthe PCB part 2002. FIGS. 2 and 3 show the state of the flexible PCB 20before it is fitted into the front frame 14, the PCB part 2002 and theerected parts 2003 being in the same plane.

As shown FIG. 5, the flexible PCB 20 comprises (i) a base film 20A, (ii)a copper foil 20B which is formed on the base film 20A and constitute'sa pattern part, and (iii) a cover lay 20C which covers the copper foil20B. The base film 20A and the cover lay 20C are made of an insulatingmaterial such as polyimide. Only the base film 20A extends out of thePCB part 2002 to form the erected parts 2003.

A resistor 2008 and a thermistor 2010 as electronic parts are installedon portions of the top surface of the PCB part 2002 corresponding to theerected parts 2003. The two light sources 22 are disposed at an intervalin a direction of the extension of the PCB part 2002, between theresistor 2008 and the thermistor 2010.

In FIG. 3, the reference numeral 2012 represents four pattern parts tobe joined to terminal parts of the light sources 22 with solder. Thereference numeral 2014 represents two pattern parts to be joined toterminal parts of the resistor 2008. The reference numeral 2016represents two pattern parts to be joined to terminal parts of thethermistor 2010.

As shown in FIG. 3, a wiring part 2004 extends from one end of the PCBpart 2002 in a direction perpendicular to the directions of extension ofthe PCB part 2002. The tip of the wiring part 2004 is provided with fourterminals 2006A to D.

The light sources 22, resistor 2008, and thermistor 2010 installed onthe flexible PCB 20 constitute the circuits shown in FIG. 6.

Namely, the two light sources 22 are connected in series and theresistor 2008 is connected in parallel with them. The resistor 2008 isconnected to the terminals 2006A and 2006B. The resistor 2008 is aprotective resistor to prevent overcurrents through the two lightsources 22.

The thermistor 2010 is provided independent of the light sources 22 andthe resistor 2008 and connected to the terminals 2006C and 2006D. Thethermistor 2010 detects the changes of temperature of the light sources22 as the changes of resistance.

The terminals 2006A to D are connected to a light-source driver circuit(not shown), which controls the light-source driving current through theterminals 2006A and 2006B based on the changes of the current throughthe terminals 2006C and 2006D.

As shown in FIGS. 1 and 2, the four optical sheets 16 are of the samerectangular shape and the same size, piled up, and put between thesupporting wall 1404 of the front frame 14 and the light-radiatingsurface 1804 of the light-guiding plate 18. The four optical sheets 16diffuse the light radiated from the light-radiating surface 1804 of thelight-guiding plate 18 and guide the light toward the liquid-crystalpanel 10.

The reflecting sheet 24 is rectangular and put on the back surface 1806of the light-guiding plate 18 and reflects the light radiated from theback surface 1806 toward the light-radiating surface 1804.

The two light sources 22 are white-light emitting diodes and constitutedas chips in the shape of a rectangular plate. Each light source 22 has alight-radiating surface 2202, which is put into close contact with theincident surface 1802 of the light-guiding plate 18.

While the first side 1808 of the light-guiding plate 18 is in contactwith the second erected wall 1408, the flexible PCB 20 and thelight-guiding plate 18 are fitted into the front frame 14. Accordingly,the light-radiating surface 1804 of the light-guiding plate 18 is put onthe four optical sheets 16 on the supporting wall 1404 and the PCB part2002 is put on the supporting wall 1404. At the time, the erected parts2003 are bent by the first erected wall 1406. Thus, the width of theerected parts 2003 is so determined that they are bent by the firsterected wall 1406 and press the light-radiating surface 2202 of thelight sources 22 to the incident surface 1802 of the light-guiding plate18.

Thus, as shown in FIG. 1, the light-guiding plate 18 is positioned withrespect to the front frame 14 in the direction defined by the incidentsurface 1802 of the light-guiding plate 18 and the first side surface1804 between the first and second erected walls 1406, and 1408 by thefirst side 1808 in contact with the second erected wall 1408 and theerected parts 2003 in contact with the first erected wall 1406. In thisstate, the elastic erected parts 2003 bent by the first erected wall1406 press the light-radiating surface 2202 of the light sources 22 tothe incident surface 1802 of the light-guiding plate 18. Namely, thelight-radiating surface 2202 of the light sources 22 are pressed to theincident surface 1802 of the light-guiding plate 18 by the elasticity ofthe erected parts 2003.

Besides, when the light-guiding plate 18 and the flexible PCB 20 arefitted into the front frame 14, the second and third sides 1810 and 1812of the light-guiding plate 18 come in contact with the second and thirdsides 1810 and 1812 of the front frame 14. Thus, the light-guiding plate18 is positioned with respect to the front frame 14 in the directiondefined between the second side 1810 and the third side 1812 of thelight-guiding plate 18.

Moreover, as shown in FIGS. 1 and 3, when the light-guiding plate 18 andthe flexible PCB 20 are fitted into the front frame 14, the erected part2003 beside the resistor 2008 is positioned between the first erectedwall 1406 of the front frame 14 and the resistor 2008/its terminal partsand the erected part 2003 beside the thermistor 2010 is positionedbetween the first erected wall 1406 of the front frame 14 and thethermistor 2010/its terminal parts.

Then, the reflecting sheet 24 is put on the back surface 1806 of thelight-guiding plate 18. Next, the rear frame 26 is put on the reflectingsheet 24 and the front and rear frames 14 and 26 are joined together.Thus, the four optical sheets 16, light-guiding plate 18, and reflectingsheet 24 are caught and fixed between the front and rear frames 14 and26. The rear frame 26 has erected strips 2602 and 2604 on its twoopposite sides, which engage, with the third and fourth erected walls1410 and 1412 of the front frame 14 to join the front and rear frames 14and 26 together. The front and rear frames 14 and 26 are electricallyconnected to the ground potential of an electronic device.

With the above construction, the back-light device 12 illuminates theliquid-crystal panel 10 as follows.

When the light sources 22 are fed with a driving current, they radiatelight from their light-radiating surfaces 2202. The light enters thelight-guiding plate 18 through its incident surface 1802 and is diffusedin various directions.

Part of the light, is guided to the liquid-crystal panel 10 through thelight-radiating surface 1804, optical sheets 16, and window 1402. Theremainder of the light goes to the reflecting sheet 24 through the backsurface 1806, is reflected by the reflecting sheet 24, passes throughthe light-guiding plate 18, and is guided to the liquid-crystal panel 10through the light-radiating surface 1804, optical sheets 16, and window1402.

Thus, the liquid-crystal panel 10 is illuminated from its back surface1004's side by the back-light device 12.

Next, the workings and effect of the back-light device 12 will bedescribed below.

As shown in FIG. 1, the two erected parts 2003 are bent by the firsterected wall 1406 of the front frame 14; accordingly, they exert forceto press the light-radiating surfaces 2202 of the light sources 22 tothe incident surface 1802 of the light-guiding plate 18, putting thelight-radiating surfaces 2202 into close contact with the incidentsurface 1802. Thus, the light radiated from the light-radiating surfaces2202 of the light sources 22 enters the incident surface 1802 of thelight-guiding plate 18 efficiently.

Besides, as the PCB part 2002 and the erected parts 2003 are formed as asingle piece, the number of parts and the cost are reduced.

Moreover, the erected parts 2003 are simply and easily bent just byfitting the flat flexible PCB 20, which has the PCB part 2002 and theerected parts 2003 in the same plane, into the front frame 14. Thus, thecost is further reduced. The erected parts 2003 may be bent before theflexible PCB 20 is fitted into the front frame 14. However, if theerected parts 2003 are bent when the flexible PCB 20 is fitted into thefront frame 14, the bent erected parts 2003 cope very easily with thedimensional error of the front frame 14 too, putting the light-radiatingsurface 2202 into closer contact with the incident surface 1802.

In addition, because the two erected parts 2003 are put into closecontact with the first erected wall 1406 of the front frame 14, the heatof the light sources 22 is conducted not only from the PCB part 2202 tothe supporting wall 1404 but also from the erected parts 2003 to thefirst erected wall 1406. Thus, the heat of the light sources 22 isdissipated efficiently.

FIG. 7 is a graph showing the relation between the ambient temperatureof the light sources 22 and the current which can be fed to the lightsources 22.

As shown in FIG. 7, if the ambient temperature of the light sources 22is reduced by improving the heat-dissipating effect as mentioned above,the current feedable to the light sources 22 is raised, giving morefreedom to the design of the back-light device 12.

As shown in FIG. 1, when the PCB part 2002 of the flexible PCB 20 is puton the supporting wall 1404 of the front frame 14, the erected part 2003beside the resistor 2008 is positioned between the first erected wall1406 and the resistor 2008/its terminal parts. Thus, the resistor 2008is separated and insulated from the front frame 14.

In the same way, when the PCB part 2002 of the flexible PCB 20 is put onthe supporting wall 1404 of the front frame 14, the erected part 2003beside the thermistor 2010 is positioned between the first erected wall1406 and the resistor 2008/its terminal parts. Thus, the thermistor 2010is separated and insulated from the front frame 14 without fail.

Thus, the resistor 2008 and the thermistor 2010 are prevented fromcoming into electric contact with the front frame 14 to cause trouble.

Now, a comparison will be made between the present embodiment and aprior art device.

FIG. 10 shows the construction of a back-light device of prior art.Since there are components identical to those in FIG. 1, like parts aregiven like reference characters and the explanation thereof will beomitted.

The back-light device of FIG. 10 differs from the present embodiment inthat the erected parts 2003 of the flexible PCB 20 are not provided.

Therefore, the light-radiating surface 2202 of the light source 22 isnot pressed to the incident surface 1802 of the light-guiding plate 18,leaving a gap between the light-radiating surface 2202 and the incidentsurface 1802. Thus, the light radiated from the light-radiating surface2202 does not enter the incident surface 1802 efficiently.

Also, the heat of the light source 22 is only conducted from the PCBpart 2002 to the supporting wall 1404. Thus, the heat of the lightsource 22 is not dissipated efficiently.

Further, the resistor 2008 and the thermistor 2010 are not reliablyprevented from coming into contact with the first erected wall 1406 ofthe front frame 14.

Thus, the present embodiment is far superior to the prior art device inthat the light from the light sources enters the light-guiding plateefficiently, the heat of the light sources is dissipated efficiently,and the insulation between the electronic parts and the frame issecured, without increasing the number of parts and the cost.

In the present embodiment, as shown in FIG. 5, the erected part 2003 isthinner than the PCB part 2002 and, therefore, a case where the erectedpart 2003 is easier to bend than the PCB part 2002 has been described.However, the present invention is naturally applied to a case where theerected part 2003 is as thick as the PCB part 2002. In such a case, partof a basal portion of the erected part 2003 may be made thin for helpingthe erected part 2003 to bend when it is fitted into the front frame 14.

FIGS. 8A, 8B, and 8C show other embodiments of the erected parts 2003 ofthe flexible PCB 20. The flexible PCB 20 of FIG. 8A has three erectedparts 2003. The flexible PCB of FIG. 8B has an erected part 2003extending along the PCB part 2002. In FIG. 8C, electronic parts areinstalled on the erected parts 2003. Further, FIGS. 8A, 8B, and 8C showthat the PCB part 2002 and the erected parts 2003 are in the same plane.

As shown in FIG. 8A, when the erected part 2003 is provided between thetwo erected parts 2003 corresponding to the resistor 2008 and thethermistor 2010, the area through which the heat of the light sources 22is conducted to the first erected wall 1406 increases compared to theone in the first embodiment. Thus, the heat of the light sources 22 isdissipated more efficiently. Also, when the three erected parts 2003 arebent by the first erected wall 1406 of the front frame 14, theelasticity which presses the light-radiating surface 2202 of the lightsources 22 to the incident surface 1802 of the light-guiding plate 18increases compared to the one in the first embodiment, putting thelight-radiating surface 2202 into closer contact with the incidentsurface 1802. Thus, the light radiated from the light-radiating surface2202 of the light source 22 enters the incident surface 1802 of thelight-guiding plate 18 more efficiently.

As shown in FIG. 8B, when there is provided the erected part 2003extending along the PCB part 2002, the area through which the heat ofthe light sources 22 is conducted to the first erected wall 1406increases compared to the example in FIG. 8A. Thus, the heat of thelight sources 22 is dissipated more efficiently. Moreover, when theerected part 2003 is bent by the first erected wall 1406 of the frontframe 14, the elasticity which presses the light-radiating surface 2202of the light source 22 to the incident surface 1802 of the light-guidingplate 18 also increases compared to the example in FIG. 8A. Thus, thelight radiated from the light-radiating surface 2202 of the light source22 enters the incident surface 1802 of the light-guiding plate 18 moreefficiently.

As shown in FIG. 8C, when electronic parts such as the resistor 2008 andthe thermistor 2010 are installed on surfaces opposite to the surfacesof the erected parts 2003 in contact with the first erected wall 1406,like in the first embodiment, the light radiated from the light sources22 enters the light-guiding plate 18 efficiently, the heat of the lightsources 22 is dissipated efficiently, the insulation between theelectronic parts and the frame is secured, and space of the PCB part2002 required for the installation of the electronic parts can bereduced. Thus, by reducing the area of the PCB part 2002, the reductionof the space and cost is achieved efficiently.

In these embodiments shown in FIGS. 8A, 8B, and 8C, also, the erectedparts 2003, may be bent and erected in advance with respect to the PCBpart 2002.

Further, in the first embodiment and other embodiments shown in FIGS.8A, 8B, and 8C, if a copper-foil pattern is formed on a portion of theerected part 2003, the heat of the light sources 22 can be conducted tothe frame 14 through the copper-foil pattern and the heat of the lightsources 22 is dissipated efficiently. The copper-foil pattern may beformed on a front surface, a back surface, or both the surfaces of theerected part 2003. Alternatively, it may be formed in the middle portionin the direction of the thickness of the erected part 2003, namely,between the base film and the overlay.

FIG. 9 shows still another embodiment of the erected part 2003 of theflexible PCB 20.

As shown in FIG. 9, in this embodiment, a reflecting material 2005 suchas a copper-foil pattern reflecting light toward the incident surface1802 (not shown in FIG. 9) of the light-guiding plate 18 is formed onthe surface of the erected part 2003 of the flexible PCB 20 facing thelight source 22.

With the above construction, as indicated by dashed lines in FIG. 9, thelight radiated from the surface opposite to the light-radiating surface2202 of the light source 22 is reflected by the reflecting material 2005to be guided to the incident surface 1802. Thus, the light radiated fromthe light source 22 enters the incident surface 1802 of thelight-guiding plate 18 efficiently.

Further, the back-light device and liquid crystal display of the presentinvention can be applied to various electronic devices such as digitalvideo cameras, digital still cameras, and mobile phones.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, it is possibleto provide a back-light device and a liquid crystal display whosemanufacturing costs are low and wherein the light from light sources isguided to a light-guiding plate efficiently and the heat of the lightsources is dissipated efficiently.

Also, according to the present invention, it is possible to provide aback-light device and a liquid-crystal display whose manufacturing costsare low and wherein the electronic parts are efficiently insulated fromthe frame.

1. A back-light device for shedding light on the back of aliquid-crystal panel, the back-light device comprising: a substantiallyrectangular light-guiding plate, the light-guiding plate including a topsurface, a bottom surface, and at least four side surfaces, the at leastfour side surfaces facing in a direction substantially perpendicular toa direction of a thickness of the light-guiding plate; wherein the atleast four side surfaces include an incident surface configured to allowlight to enter and a first side surface opposite the incident surface;and wherein one of the top and bottom surfaces of the light-guidingplate is a light-radiating surface; a flexible PCB (printed circuitboard) attached to part of the light-guiding plate in a vicinity of theincident surface; a plurality of light sources installed on the flexiblePCB, each of the plurality of light sources including a light-radiatingsurface which contacts the incident surface of the light-guiding plate;and a frame configured to house and hold the light-guiding plate and theflexible PCB, wherein the frame includes a supporting wall configured tosupport the light-guiding plate, a window provided in the supportingwall and through which the light-radiating surface of the light-guidingplate is seen, and erected walls which are erected at the periphery ofthe supporting wall; wherein the erected walls include a first erectedwall substantially perpendicular to the supporting wall, and a seconderected wall substantially perpendicular to the supporting wall andlocated opposite the first erected wall; wherein the flexible PCBincludes a PCB part on which the light sources are installed and erectedparts which are erected on the far side of the PCB part away from theincident surface of the light-guiding plate; wherein the light-guidingplate is positioned in the frame such that the first side surface of thelight-guiding plate contacts the second erected wall; and wherein theflexible PCB is positioned in the frame such that the erected partscontact the first erected wall of the frame and the flexible PCB biasesat least one of the plurality of light sources against the incidentsurface of the light guiding plate.
 2. A back-light device according toclaim 1, wherein the light-radiating surface of the light source ispressed to the incident surface of the light-guiding plate by theerected parts.
 3. A back-light device according to claim 1, whereinelectronic parts including exposed terminals are installed on the PCBpart in the vicinity of the erected part of the flexible PCB.
 4. Aback-light device according to claim 1, wherein the heat from theplurality of light sources is conducted to the first erected wall of theframe through the erected part of the flexible PCB.
 5. A back-lightdevice according to claim 1, wherein a copper-foil pattern is formed ona front surface or a back surface of the erected part of the flexiblePCB.
 6. A back-light device according to claim 1, wherein a copper-foilpattern is formed in a middle portion of the erected part of theflexible PCB in the of a thickness of the flexible PCB.
 7. A back-lightdevice according to claim 1, wherein a reflecting material reflectinglight to the incident surface of the light-guiding plate is provided ona surface of the erected part of the flexible PCB facing the pluralityof light sources.
 8. A back-light device according to claim 1, whereinthe flexible PCB is pasted onto the top surface or the bottom surface ofthe light-guiding plate in the direction of the thickness of thelight-guiding plate.
 9. A back-light device according to claim 1,wherein electronic parts are installed on a surface of the erected partsopposite to a surface of the erected parts in contact with the firsterected wall of the frame.
 10. A back-light device according to claim 1,wherein the light-guiding plate includes second and third side surfacesopposite to each other between the incident surface and the first sidesurface, wherein the supporting wall of the frame is substantiallyrectangular; wherein the erected walls include a third erected wall anda fourth erected wall, the first, second, third and fourth erected wallserected on four sides of the supporting wall, the first and seconderected walls facing each other and the third and fourth erected wallsfacing each other; wherein the light-guiding plate is positioned in theframe such that the first side surface is in contact with the seconderected wall and the second and third side surfaces are in contact withthe third and fourth erected walls, respectively.
 11. A back-lightdevice according to claim 1, wherein the frame further comprises a frontframe including the supporting wall, the window, and the erected wallsand a rear frame covering the top or bottom surface of the light-guidingplate and the flexible PCB on the opposite surface of the light-guidingplate in the direction of the thickness of the light-guiding plate andjoined to the front frame.
 12. A back-light device according to claim 1,wherein the first side surface of the light-guiding plate opposite tothe incident surface is in contact with the first erected wall of theframe and the flat flexible PCB and the light-guiding plate are fittedinto the frame, and wherein a width of the erected parts of the flexiblePCB include a width such that the erected parts are bent with respect tothe PCB part by the first erected wall of the frame and press thelight-radiating surface of the light source to the incident surface ofthe light-guiding plate.
 13. A liquid crystal display comprising aliquid-crystal panel and a back-light device for shedding light on theback of the liquid-crystal panel, the back-light device comprising: asubstantially rectangular light-guiding plate, the light-guiding plateincluding a top surface, a bottom surface, and at least four sidesurfaces, the at least four side surfaces facing in a directionsubstantially perpendicular to a direction of a thickness of thelight-guiding plate; wherein the at least four side surfaces include anincident surface configured to allow light to enter and a first sidesurface opposite the incident surface; and wherein one of the top andbottom surfaces of the light-guiding plate is a light-radiating surface;a flexible PCB attached to part of the light-guiding plate in a vicinityof the incident surface; a plurality of light sources installed on theflexible PCB, each of the plurality of light sources including alight-radiating surface which contacts with the incident surface of thelight-guiding plate; and a frame configured to house and hold thelight-guiding plate and the flexible PCB, wherein the frame includes asupporting wall configured to support the light-guiding plate, a windowprovided in the supporting wall and through which the light-radiatingsurface of the light-guiding plate is seen, and erected walls which areerected at the periphery of the supporting wall; wherein the erectedwalls include a first erected wall substantially perpendicular to thesupporting wall, and a second erected wall substantially perpendicularto the supporting wall and located opposite the first erected wall;wherein the flexible PCB includes a PCB part on which the light sourcesare installed and erected parts which are erected on the far side of thePCB part away from the incident surface of the light-guiding plate;wherein the light-guiding plate is positioned in the frame such that thefirst side surface of the light-guiding plate contacts the seconderected wall; and wherein the flexible PCB is positioned in the framesuch that the erected parts contact the first erected wall of the frameand the flexible PCB biases at least one of the plurality of lightsources against the incident surface of the light guiding plate.
 14. Aliquid crystal display according to claim 13, wherein thelight-radiating surface of the light source is pressed to the incidentsurface of the light-guiding plate by the erected parts.
 15. A liquidcrystal display according to claim 13, wherein electronic partsincluding exposed terminals are installed on the PCB part in thevicinity of the erected part of the flexible PCB.
 16. A liquid crystaldisplay according to claim 13, wherein heat from the plurality of lightsources is conducted to the first erected wall of the frame through theerected part of the flexible PCB.
 17. A liquid crystal display accordingto claim 13, wherein a copper-foil pattern is formed on a front surfaceor a back surface of the erected part of the flexible PCB.
 18. A liquidcrystal display according to claim 13, wherein a copper-foil pattern isformed in a middle portion of the erected part of the flexible PCB inthe of a thickness of the flexible PCB.
 19. A liquid crystal displayaccording to claim 13, wherein a reflecting material reflecting light tothe incident surface of the light-guiding plate is provided on a surfaceof the erected part of the flexible PCB facing the plurality of lightsources.
 20. A liquid crystal display according to claim 13, wherein theflexible PCB is pasted onto the top surface or the bottom surface of thelight-guiding plate in the direction of the thickness of thelight-guiding plate.
 21. A liquid crystal display according to claim 13,wherein electronic parts are installed on a surface of the erected partsopposite to a surface of the erected parts in contact with the firsterected wall of the frame.
 22. A liquid crystal display according toclaim 13, wherein the light-guiding plate includes second and third sidesurfaces opposite to each other between the incident surface and thefirst side surface, wherein the supporting wall of the frame issubstantially rectangular; wherein the erected walls include a thirderected wall and a fourth erected wall, the first, second, third andfourth erected walls erected on four sides of the supporting wall, thefirst and second erected walls facing each other and the third andfourth erected walls facing each other; wherein the light-guiding plateis positioned in the frame such that the first side surface is incontact with the second erected wall and the second and third sidesurfaces are in contact with the third and fourth erected walls,respectively.
 23. A liquid crystal display according to claim 13,wherein the frame further comprises a front frame including thesupporting wall, the window, and the erected walls and a rear framecovering the top or bottom surface of the light-guiding plate and theflexible PCB on the opposite surface of the light-guiding plate in thedirection of the thickness of the light-guiding plate and joined to thefront frame.
 24. A liquid crystal display according to claim 13, whereinthe first side surface of the light-guiding plate opposite to theincident surface is in contact with the first erected wall of the frameand the flat flexible PCB and the light-guiding plate are fitted intothe frame, and wherein a width of the erected parts of the flexible PCBinclude a width such that the erected parts are bent with respect to thePCB part by the first erected wall of the frame and press thelight-radiating surface of the light source to the incident surface ofthe light-guiding plate.